1. Field of the Invention
The present invention relates to a method of growing lutetium oxyorthosilicate crystals and in particular to a method for growing such crystal for use as scintillator. The invention also provides improved scintillation detectors incorporating such crystals.
2. Description of the Prior Art
Cerium doped lutetium oxyorthosilicate crystals are known to be useful as scintillators for .gamma. ray and x-ray detectors. U.S. Pat. No. 4,958,080 and U.S. Pat. No. 5,025,151 (both incorporated herein by reference) describe a single crystal scintillator formed from a melt of formula Ce.sub.2x Lu.sub.2(1-x) SiO.sub.5, wherein 2.times.10.sup.-4 &lt;.times.&lt;3.times.10.sup.-2 (hereinafter the term LSO will be used as shorthand for this formula). The method proposed for growing LSO is the Czochralski crystal growth method which is generally described in the publication CRYSTAL GROWTH: A TUTORIAL APPROACH, W. Bardsley, D. T. J. Hurle, J. B. Mullins (eds) North-Holland Publishing Company, 1979, pp 189-215. This method has been used for growing scintillator crystals as is described in "Growth and applications of Gd.sub.2 SiO.sub.5 :Ce scintillators" T. Utsu and S. Akiyama, Journal of Crystal Growth 109 (1991) 385-391 for gadolinium orthosilicate scintillators and in "Czochralski growth of rare earth oxyorthosilicate single crystals" C. L. Melcher, R. A. Manente, C. A. Peterson and J. S. Schweitzer, Journal of Crystal Growth 128 (1993) 1001-1005, and "A Macintosh-based System For Czochralski Crystal Growth" C. L. Melcher, R. A. Manente, C. A. Peterson, J. S. Schweitzer, M. A. Singelenberg and F. J. Bruni, Scientific Computing and Automation, January 1994 39-45 for LSO scintillators.
While these methods can be used to make scintillator crystals which are useful in certain applications, there is variability between the scintillation behavior of different crystals cut from a single boule of LSO. This variability has not been seen in any other property than the scintillation behavior, i.e. to all other intents and purposes, the boule appears to be homogenous, but the resulting crystals have .gamma.-ray spectra with broad or multiple peaks. However, for spectroscopic uses of LSO crystal scintillators, it is desirable that the behavior be as uniform as possible.
It is an object of the present invention to provide a method for producing LSO crystals for use as scintillators which display substantially uniform scintillation behavior throughout the crystal.
It is another object of the present invention to provide an improved Czochralski crystal growth method for producing LSO crystals.